Intermittent inductive train control system



5 Sheets-Sheet 1 ATTORNEY W. H. REICHARD INTERMITTENT INDUCTIVE TRAINCONTROL SYSTEM Filed March 23, 1956 Feb. 22, 1938.

Feb. 22, 1938. w. H. REICHARD INTERMITTENT INDUCTIVE TRAIN CONTROLSYSTEM Fil ed March 23, 1936 5 Sheets-Sheet 2 aka 1 FIGZ.

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INVE T K- AETORNEY I Feb. 22, 1938. w. H. REICHARD I 2,109,154

INTERMITTENT INDUCTIVE TRAIN CONTROL SYSTEM Filed March 23, 1956 5Sheets-Sheet 5 TBi 44% TTORNiEY J Feb. 22, 1938. w. REICHARDINTERMITTENT INDUCTIVE TRAIN CONTROL SYSTEM Fi led March 25, 1936 V 5Sheets-Sheet 4 Feb. 22, 338. W. H. REIC'HARD 2,109,154

v INTEBMITTENT INDUCTIVE TRAIN CONTROL SYSTEM Filed March 25, l936 5Sheets-Sheet 5 FBGOMZ Patented Feb. 22, 1938 UNITED STAES ATE? EQEINTERMITTENT INDUCTIVE TRAIN CON- TROL SYSTEM Application March 23,1936, Serial No. 70,259 28 Claims. (01. 246-63) This invention relatesto automatic train control systems for railroads, and more particularlyto an intermittent inductive system of the inert track element typewhich provides a distinctive indication of clear, in addition toacaution and stop control.

The general underlying purpose or object of this invention is to obtain,in a safe and eflicient manner, a distinctive indication of clear, aswell as restrictive indications or controls of caution or stop, orneither, at the same or different track locations, by the intermittentinductive co-operation of a receiver carried on a railway vehicle andinductors located on the track, which comprise simple magnetic cores andcoils energized only from a source of alternating current on thevehicle, and which provide an organization in which the receiver on thevehicle will not be adversely influenced by extraneous magnetic fieldsor masses of iron along the track, and in which transmission of theindications or controls is effective, without changing circuitconnections or the like, for movement of the vehicle in either directionpast the inductor location, or with either end of the vehicle ahead.

Generally stated, and without attempting to define the exact nature andscope of the invention, the receiver on the vehicle comp-rises alaminated magnetic core, having coils thereon in a resonant circuitenergized from a source of alternating current on a vehicle of arelatively high frequency, together with a suitable quick-actingelectro-responsive means responsive to the intensity o-f current in thiscircuit. The track inductor comprises a similar laminated magnetic corewith which the receiver core is magnetically coupled as the vehiclepasses the inductor location; and the track inductor core is providedwith coils and circuits to control its effect upon the receiver, suchthat the electro-responsive means may be effectively de-energized ormaintained energized to provide for the transmission of a restrictiveindication or control when desired, in accordance with trafiicconditions, or the indica- -i5 tions of an associated wayside signal. Inthe preferred form of the invention, two such cores in the receiver andin the track inductor are employed to act independently to transmitdistinctive indications or controls of caution and stop at 50 the sameor difierent inductor locations. The receiver also comprises anadditional laminated magnetic core, disposed so as to have the minimumof magnetic coupling with the other receiver core or cores, and havingcoils thereon 55 connected to a suitable quick-acting electro-rcsponsivemeans to register an indication of clear; and the track inductorcomp-rises a similar additional laminated core with coils thereon sodisposed as to be magnetically coupled with the additional core of thereceiver as the vehicle passes 5 an inductor location. Under clearconditions, when a circuit on the trackway is closed, energy istransferred from; the receiver to the track inductor through the samecore or cores and coils producing the caution or stop control; and this10 energy is then reflected back from the additional core and coils ofthe inductor to the additional core and coils of the receiver, suchreflected energization actuating the clear electro-responsive means. 15

Various other characteristic features, attributes and advantages of theorganization of parts and circuits constituting the invention will be inpart apparent, and in part pointed out, as the description progresses.20

In the accompanying drawings, which illustrate certain specificembodiments of the invention which are, of course, susceptible ofvariation and modification in accordance with the results desired, Fig.1 is a diagrammatic representation 25 of the parts and circuitsconstituting the vehicle equipment and trackway equipment, these partsand circuits being shown in, the manner to facilitate an understandingof the invention, rather than to show the particular construction andar- 30 rangement of parts preferably employed in practice; Figs. 2 and 3are plan and side views respectively of the preferred construction ofthe carcarried receiver; Fig. 4 illustrates one particular arrangementof track inductors and their control 35 circuits for home and distantsignals; Fig. 5 illustrates a modification of the receiver and inductor;and Figs. 6 and 7 illustrate two different specific arrangements ofparts and circuits for utilizing the caution and stop controls for safe-40 guarding train operations.

Referring to Figs. 1, 2 and 3, the inductive device carried on thelocomotive or car, and conveniently termed a receiver in the particularorganization shown comprises two spaced magnetic cores A and B,laminated in accordance with the usual practice, and disposed parallelto the trackway. These cores A and B preferably have the general shapeand proportions shown in Figs. 2 and 3. Each of these cores A and Bthasthereon two coils Al, A2, and Bi, B2 of the usual construction. Thereceiver also comprises a transverse laminated magnetic core C, with twocoils Cl and C2 thereon. This transverse core C is disposed at rightangles to the cores A and B, so

as to have the minimum magnetic coupling with said cores A and B.Laminated pole pieces 5, extending parallel with the track and withtheir lower faces substantially in the same plane as the lower faces ofthe ends of cores A and B, are preferably attached in a suitable manner,as by clamps and bolts to the ends of this transverse core C. Thetransverse core C also is preferably provided with a middle pole piece6, likewise extending longitudinally of the track parallel with thetrack A and B, and approximately twice the cross section of the end polepieces 5. The receiver, as shown in Fig. 2, may also include a middlenarrow longitudinal stabilizing core 1 of laminations, which is usefulunder certain conditions as a flux stabilizer, but may be omitted.

These cores A, B and C of the receiver are in practice rigidly supportedand housed in a suitable non-magnetic casing (not shown), which isadjustably hung from a wheel truck or the body of the locomotive or carat a height to provide the desired clearance over the track rails atswitch points and crossings and other bodies between the tracks, and atsuch a height as to provide a suitable working air-gap with the trackinductor. In one typical arrangement, the receiver is supported with thelower faces of its cores approximately 5 inches above the level of thetop of the track rails. The receiver is also preferably disposedsymmetrically on the center line of the car, although it may beotherwise located on the car where space and clearance permit.

Referring to Figs. 1 and 2, the coils Al and A2 of the longitudinal coreA of the receiver are connected in series in a circuit including acondenser 8, an impedance 9, and a suitable source of alternatingcurrent, such as a steam turbo-generator TG, preferably of a relativelyhigh frequency such as 360 cycles per second. The coils Al and A2 are sowound and connected as to produce magnetic lines of force or fluxthrough the core A in the same direction. The condenser 8 is adjusted orselected so that the circuit is substantially resonant at the normalfrequency, when the receiver is not over the track inductor.

The terminals of the impedance 9 are connected to the input terminals ofa suitable double wave rectifier l0, shown conventionally, andpreferably of the metallic or copper-oxide type; and the outputterminals of this rectifier ID are connected to a direct currentelectro-responsive device in the form of a relay RA, preferably with aseries resistance I I for the purpose to be explained later.

The coils BI and B2 of the other longitudinal core B of the receiver areconnected in a similar manner in a resonant circuit including acondenser l2 and impedance I3, and the same source of current TG, andcontrol the energization of the similar relay RB through a double-waverectifier l4 and resistance IS.

The coils Al, A2 and the coils Bl, B2 on the two longitudinal cores Aand B are so wound and connected as to produce magnetic lines of forceor flux in the same direction in the two cores A and B, as indicated bythe arrows a for a given instant.

The relays RA and RB are each preferably a two coil structure with anarmature pivoted at its center of mass, so as to be substantially immuneto all jar and vibration, the biasing force to actuate the armature toits retracted position upon de-energization of its windings beingprovided by a suitable spring. Each relay RA and RE is preferably soconstructed or adjusted that,

upon movement of its armature to its retracted position, the normalenergizing current will not be sufficient to attract the armature again.In other words, the relay has locking or stick characteristics whende-energized due to its inherent magnetic construction, this beingconsidered pref erable to an electrical stick relay, which may be usedas desired, because it makes the operating characteristics of the relaymore suitable for a .quick response to a momentary change in itsenergizing current.

The coils C 1, C2, on the transverse core C of the receiver are arrangedto supply voltage to a normally de-energized and inactive quick-actingdevice for giving a clear indication. On account of the relatively smallenergy change occurring upon transmission of the clear indication, andthe rapid response necessary at high speeds of train movement, thisclear responsive device preferably comprises an electronic tube of themercury vapor or gas filled type, which is rendered conductive, or firedso to speak, by an increase in its grid potential above a criticalvalue, this tube also having the operating feature characteristic of itstype that, once conductive or fired by an increase in grid potential,remains in that condition even after the grid potential is restored tonormal, until the tube is restored to its non-conductive condition byinterrupting its plate circuit or the like. Electronic tubes of the typecontemplated are well known in the art; and one form well adapted foruse in this invention is commonly known as a positive grid controlledThyraton.

In the preferred arrangement shown in Fig. 1, the coils Cl, C2 areconnected in series with a condenser I8 to the primary of a smallcoupling transformer l9, this primary circuit being tuned for afrequency double the frequency of the turbogenerator TG. The secondaryof the transformer I9, tuned by a condenser 20 for maximum terminalvoltage at this double frequency is connected to the grid circuit of thetube VT. As shown, the heating element or filament of this tube issupplied with current from a battery; and

the plate circuit of this tube is energized from another battery. Ifdesired current derived from the turbo-generator -TG through rectifiers,with such a transformer as necessary to change the voltage, may beemployed instead of these batteries, a condenser across the rectifierbeing preferably employed to maintain an effective potential on theplate of the tube at all instants.

In the arrangement illustrated in Fig. 1 as typical of the invention, anelectrical lamp G of the usual type is included in the plate circuit ofthe tube VT, so as to be lighted to display a proceed indication whenthe tube is fired. A suitable hand switch or key K is provided to openvthe plate circuit of the tube manually, and extinguish the lamp G, suchmanual manipulation being an act of recognition or acknowledgment of theclear indication. In this connection, a suitable time element device maybe employed, as later described, to extinguish the lamp G automat icallyafter a time interval.

The track inductor comprises the same general organization oflongitudinal cores TA and TB, a transverse core TC, and coils TAI, TA2,coils TBI, TBZ, and coils TCI and TC2 as the receiver; and forconvenience in manufacture the same laminations may be employed toconstruct the receiver and track inductor. The cores and coils of thetrack inductor are rigidly supported in a suitable housing ofnon-magnetic material, preferably with ramped ends to deflect draggingequipment; and on electrified railroads employing a central contactrail, the inductor housing may be supported on insulators, and may beequipped with a wear resisting surface to cooperate with the contactshoe of the car or locomotive. These, and various other details ofconstruction preferably employed in practice, have not been specificallyillustrated.

The coils TA! and TA?! on the longitudinal core TA of the track inductorare connected in series to a control circuit. ment, these coils areconnected to the terminal of a stop condenser 2|. The coils TBi, T132 onthe other longitudinal core TB of the track inductor are similarlyconnected to a stop condenser 22. The coils TCI and TCZ of thetransverse core T0 of the track inductor are connected in series to acircuit for transmitting the clear indication.

In the preferred arrangement for transmis' sion of a clear indication,which involves use of a frequency double the frequency of thevehiclecarried source TG, these coils TCI and T02 are connected to theterminals of a double-wave rectifier 24, preferably of the metallic orcopperoxide type, the other terminals of which are connected in serieswith a condenser 23 to the secondary of a transformer 25. The primary ofthis transformer 25 is adapted to be connected in series with a clearcondenser 25 to the coils TAl, TAEE, FBI and THE, under the control ofcontacts for governing the character of indication to be transmitted,such that the coils TC! and T02 are energized under clear conditions, atdouble the frequency of the vehicle-carried source, by energytransmitted from the car to the track, in a manner to be explained morein detail later. In the simplified arrangement shown in Fig. l, thecontacts governing the condition of the track inductor are shown in theform of a movable switch arm 27, movable to any one of three differentpositions.

With this explanation of a general organization and arrangement of partsand circuits constituting the invention, consideration may now be givento the contemplated operation of the system.

Under normal conditions, while the vehicle is traveling between inductorlocations, the parts and circuits on the vehicle are as shown in Fig. l.The coils Al, A2, and Bi, B2 are energized with alternating current incircuits tuned to resonance by the condensers 8 and I2, so that amaximum current flows throughthese coils.

The drop of potential across the impedances 9 and i3 supply voltage tothe rectifiers l0 and M, which in turn supply unidirectional current toenergize the relays RA and RB.

Due to the transverse arrangement of the core C or" the receiver, thereis no direct magnetic coupling between this core and the longitudinalcores A and B. Also, the coils Cl and C2 are so wound with the samenumber of turns and connected in series on the core 0 that, ifenergized, they tend to produce fluxes in opposite directions asindicated by the arrows 1).. Thus, magnetic lines of force passingthrough these coils C! and C2 in the same direction induce opposingvoltages. Consequently, any leakage fluxes from the cores A and B tendto produce opposing voltages in the coils Cl and C2. The net result isthat there is substantially no normal voltage in the coils Cl and C2.

In the preferred embodiment of the invention illustrated, the receivercore A, co-operating with In the preferred arrange the inductor core TA,acts to control the energization of the relay RA independently of thecontrol of the relay RB by the co-operation of the other receiver core Band inductor core TB. As already noted, the magnetic flux produced inthe longitudinal receiver cores A and B by their coils is in the samerelative direction as indicated by the arrows a. for a given instant;and the parts are so designed and proportioned that these fluxes aresubstantially equal. The transverse spacing of the longitudinal receivercores A and B is made several times the normal working air-gap betweenthe receiver cores and inductor cores, the spacing in one typicalarrangement being about H inches for a working air gap of 3 inches. Themagnetic independence between the longitudinal receiving cores A and Bis further assured by the longitudinal stabilizing middle core 1 shownin Fig. 2. In short, the two pairs of longitudinal receiver and inductorcores comprise independently acting and du plicate indication or controltransmitting instrumentalities; and since the operation of each of theseduplicate units is the same, a discussion of one will sufiice for both.

According to the contemplated operation, when the longitudinal core ofthe receiver comes over its co-operating track core TA, with the coilsTAI and TA2 thereon on open circuit, or connected to a stop condenser ofproper capacity, the current normally flowing in the receiver coils Al,A2 is greatly reduced, and the relay RA is effectively de-energized torelease its armature. There seems to be several electrical and magneticphenomena involved in thus producing such reduction in the normalenergizing current for the receiver coils A! and A2, so that it isdifiicult to attribute the results obtained to any one simple action.

According to one theory of operation, the receiver circuit through thecoils Al,,A2 is substantially resonant under normal conditions when thereceiver is not over the track inductor; but when the receiver core Aismagnetically coupled to the inductor core TA, the resonant condition ofthe receiver circuit is destroyed, and losses are reflected into thiscircuit, so that there is a large change in the normal current. Amongother things, the presence of the inductor core TA may be considered aschanging the magnetic reluctance of the receiver core A, and hence theinductive reactance cf the receiver coils Al and A2, thereby disturbingthe critical resonant condition of the receiver circuit and reducing thecurrent therein. The presence of the inductor core TA also seems to havethe efiect of reflecting additional losses into the receiver circuit,likewise tending to reduce the current intensity in this circuit.

In this connection, it is apparent that the more sharply this receivercircuit is tuned, the greater will be the decrease in current for agiven change in the inductive reactance in this circuit. The magneticcharacteristics of the iron and thickness of the laminations of thereceiver core, the emciency of the tuning condenser, and the proportionsof the coils on this core are chosen so that the receiver circuit as aWhole has relatively small efiective resistance losses and may be tunedsharply, With due regard to its stability for the small variations inthe frequency or the turbo-generator that must be expected in practice.

It is found that this range of current change produced by the trackinductor core TA is materiall increased by connecting the coils TAI, TA2on this inductor core to a stop condenser 2| of the proper capacity,apparently because the current which then circulates in the coils TAI,TA2, and the magnetic flux associated with such circulating current, hasa reaction on the receiver core and coils, perhaps due to its time phaserelation, which reduces the current in the receiver circuit moreeffectively than if the inductor coils are on open circuit. Accordingly,such a stop condenser 2| of the proper capacity, permanently connectedacross the inductor coils, is preferably employed so as to obtain awider range of current change than the inductor core alone would give,even though the inductor core without such stop condenser connected toits coils causes a reduction in the normal energizing current of therelay amply suflicient to release its armature.

The proportions of the parts, the frequency employed, and otherconditions of course modify in some degree the operation and the resultsobtained; and it should be understood that the foregoing is merely atheoretical explanation of the phenomena to which the results obtainedin practice are attributed. As an indication of the effectiveness of thetype of inductive control provided by this invention, it may be statedthat,

with a typical arrangement of parts and a frequency of about 360 cyclesper second, a normal current in the order of two amperes may be reducedto substantially zero with an air-gap of about 3 inches between thereceiver and inductor.

When it is desired to render the inductor core TA ineffective to causesuch de-energization of the relay RA, the coils TAI, TAZ of the inductorare preferably short-circuited, although a similar non-effectivecondition of the inductor core may be obtained by connecting these coilsto a condenser of suitable large capacity, or to a condenser andreactance in series. Under these conditions, when the core A of thereceiver passes over the core TA of the inductor, the disturbance of theresonant condition and the reflection of energy losses is small, andthere is only a small change in the normal current through the receivercoils Al, A2, something in the order of 10 per cent. The operatingcharacteristics of the relay RA are readily chosen, so that thisrelatively small reduction of current is not sufficient to cause thisrelay to release its armature.

This non-effective condition of the inductor core, produced byshort-circuiting the coils TAI, TA2 on this core, is attributed, amongother things, to the choking effect of the circulating current in thesecoils, which tends to reduce the magnetic flux of the receiver corepassing through the inductor core, and thus reducing its influence uponthe receiver circuit. There may be other contributing factors to beconsidered in a precise theoretical analysis of the operation; but thegeneral effect is that short-circuiting the coils TAI, TA2 on the trackinductor core TA render it ineffective to cause de-energization of therelay RA.

Thus, in accordance with this invention, the relay RA is not deenergizedeffectively, during the passage of the receiver, if the coils TAI, TA2on the inductor core are short-circuited; but if these coils are on opencircuit or connected to a stop condenser 2|, there is a great change inthe normal energizing current for the relay RA,

relay RA on the vehicle may be maintained energized, or may bede-energized upon passing over the track inductor, thereby providing forthe transmission of a restrictive indication or control underunfavorable traflic conditions, as may be required.

The same plan and theory of operation for relay RA applies to the relayRB; and either one,

or both, or neither of distinctive restrictive indications may-beproduced on a railway vehicle at an inductor location. In one typicalarrangement, considered more in detail later, itis contemplated that acaution condition is obtained when either one of the relays RA or RB isdeenergized, and a stop control when both of these relays aresimultaneously de-energized.

Considering now the operation of the system of transmitting anindication of clear, theinductor coils TAI, TA2 and TBI and TB2 areconnected together in series with the clear condenser 26 under clearconditions. Thus, if the switch 21 is in the clear position shown, acircuit for current to circulate through the coils TAI, TA2 and TBI andT132 in series may be traced from one terminal of coil TA2, wires 30,3|, 32, 33, coil TBI, wire 34, coil TBZ, wires 35 and 36, switch 21 inclear position shown, wire 31, clear condenser 26, wire 38, primary oftransformer 25, wires 39 and 40, coil TAI, wire 41, back to coil TAZ.

In this connection, it should be understood that the coils TAI, TA2, andTB], TB2 are so wound on the respective inductor cores TA and TB and soconnected that the voltages induced in these coils by the alternatingflux produced in said cores by induction from the cores A and B of thereceiver, will be in the same direction or cumulative. In other words,when the receiver cores A and B come over the inductor cores TA and TB,the magnetic fluxes in the cores A and B in the same direction asindicated by arrows a, pass through the coils TAI, TAZ, TBI and T132 andinduce voltages therein, and these several coils of the inductor are sowound and connected that these voltages add together.

The current thus produced in-the primary of the transformer 25 induces avoltage in the secondary which supplies current through a double waverectifier 24 to the coils TC! and TC2 on the transverse core TC of thetrack inductor, preferably with a series condenser 23 to obtain themaximum circulating current.

Since the voltages induced in the coils TAI, TAZ, TBI and TB2 areordinarily relatively high in an organization of parts in accordancewith this invention, the transformer 25 is used to reduce this voltageto lit the voltage limitations of the rectifier 24, assuming the use ofrectifiers of the metallic or copper-oxide type. Due to this double-waverectifier 24, voltage pulses in the same direction are applied to thecoils TCI, TC2 at double the frequency of the voltages which are inducedin the inductor coils from the receiver.

While the receiver is passing over the inductor,

the transverse core C of the receiver is magnetically coupled with thetransverse core TC of the inductor; and the current circulating in theinductor coils. TCI, TC2 produces opposing fluxes in opposite directionsas indicated by thearrows 0 for a given instant, which pass through thecoilsCl, C2 of the receiver in opposite directions, indicated by thearrows b for the same instant, and thereby induce therein cumulativevoltages. The pole pieces 5 and l on the transverse cores C andTC of thereceiver and inductor aid in prolonging the duration of this transfer ofenergy.

The voltage thus induced in the receiver coils Cl and C2 produces acirculating current through the primary of the transformer [9, thecondenser l8 being provided to make this circulating current a maximumat the double frequency; and the current in this primary in turn inducesa voltage in the secondary, which is tuned for the double frequency bythe condenser 20, so as to have the maximum terminal voltage. Thisterminal voltage is applied to the grid of the tube VT and makes thisgrid sufficiently positive with respect to its filament or heatingelement that the tube is rendered conductive, and current flows in theplate circuit to light the lamp G. This tube has a structuralarrangement of elements, or is otherwise so designed, that it maintainsthis 'fiow of plate current even after the voltage applied to the gridhas ceased. The hand switch or push button K, located within convenientreach of the engineman or driver, is operated by him to open the platecircuit to extinguish the lamp G.

The clear indication provided by this invention is intended to conveyinformation to the engineman or driver that he has passed a signalindicating clear, this being particularly useful in case of dense fog orother unfavorable weather conditions where the engineman may not be ableto see the signal clearly. The purpose of the caution and stop controlor indications is to inform the engineman that he has passed a cautionor stop signal, and also to enforce such acknowledgment or automaticcontrol of the brakes of the train as may be desired.

It is a fundamental principle in automatic train control that as far aspracticable the apparatus and circuits should be so organized andarranged that a broken wire, failure of asource of energy, or the like,should be on the side of safety. In the case of restrictive indicationsor controls, such as caution or a stop, it is desirable to providecircuits and devices which are normally energized, and which arede-energized to produce the desired effect, so that any broken wire,failure of energy or contacts, or the like, will cause a condition onthe side of safety, and will not show proceed condition which may not betrue.

This principle, sometimes called the normally closed circuit principle,is carried out in this invention. Relays RA and RB are normallyenergized, and if the turbo-generator fails, or a wire breaks, the relayBA or BB is de-energized. Since the circuit for energizing each relay RAor R13 is tuned to resonance, a break-down of the tuning condenser, or ashort circuit of one or both of the coils on the receiver, will destroythe resonant condition of the circuit and cause de-energization of therelay.

Also, the desired restrictive indication is produced by the magneticqualities of the inert cores of the track inductor; and no reliance isplaced upon any supply of current on the trackway or continuity of acircuit, or a permanent condition of a magnet to produce the caution orstop control.

In this connection, it should be understood that the stop condenser,which is preferably employed for reasons already stated, is not reliedupon to produce the caution or stop control; and if this circuit shouldbe broken, the inherent magnetic qualities of the inductor cores cause asufficient reduction in the normal energizing ourrent for the relays RAor RB to assure retraction of their armatures for all ordinary operatingconditions. The stop condenser gives an additional range of controlwhich it is considered desirable to use.

The non-restrictive indication at an inductor location is produced byclosing a circuit of low resistance around the inductor coils; and anybreak or contact failure in this circuit is a failure on the side ofsafety, since a restrictive indication is transmitted in the event ofsuch failures.

In the case of a clear indication, however, it is desirable to utilizean organization of normally de-energized circuits and normally inactivedevices, such that a broken wire, failure of energy, or the like, willnot cause an improper clear indication, but rather prevent thetransmission of such a clear indication. In other words, an indicationof clear should not be obtained unless the circuits and all the partsare functioning properly. Thus, the tube VT is arranged to require theapplication of voltage to light the lamp; and the circuit through thecoils Cl and C2 of the receiver is normally de-energized, and receivesits energy at inductor locations only by inductive transfer of energyfrom the track. Such transfer of energy will occur only if the circuitson the track are functioning properly.

In this connection, the transformer 25, rectifier 24, and the electricalconnections described, are employed to double the frequency; and theclear indication receiving circuit, including the transformer I9 andcondensers I8 and 20, is tuned so as to be responsive only to suchdouble frequency. This avoids the chance of an improper clear indicationby transfer of energy from the car alone, and requires co-operation withtrack devices. This arrangement for employing double frequency for aclear indication is considered to be an important feature of theinvention.

Also, the clear indication transmitting coils TC I TCZ on the trackinductor are so wound that they create opposing fluxes which at a giveninstant, when the receiver is passing over the track inductor, may beconsidered as projecting upward from the middle of the transverse trackcore TC into the middle of the receiver transverse core C, and thensidewise in opposite directions through the clear indication receivingcoils CI, C2.

This particular direction of flux through the 7 receiver coils Cl, C2 isnecessary to induce cumulative voltages. This arrangement makes theclear indication coils Ci, C2 of the receiver immune to extraneous fluxfields that might be encountered along the railroad track, since thelines of force from such extraneous fields. would out both coils in thesame direction, and the voltages induced thereby would counter-act eachother. Thus, the magnetic fields of power conductors or magnetizedbodies along the track will not cause an improper indication of clear.

Since the restrictive indications are produced by magnetic qualities ofthe inert inductor cores, the receiver is susceptible in a degree to theinfluence of extraneous magnetic bodies along the track between thetrack rails, such as covers for signal or switch point operatingapparatus, water pans, and the like. Such extraneous magnetic bodies areordinarily at such a distance below the receiver, as compared with theinductor, that their influence on the receiver is not significant. Also,on account of the relatively high frequency employed, such extraneousiron masses along the track do not affect the receiver as much as thelaminated inductor cores; and even when acting through the same air-gapsuch as the inductor cores, such extraneous magnetic bodies fail toproduce a sufiicient reduction in the normal relay energizing current torelease their armatures. This, of course, is a matter of degree; and insome instances it may be desirable to reduce further the effect of suchextraneous magnetic bodies by employing a shield of a copper plate orthe like, which due to the effect of eddy current losses renders suchextraneous magnetic bodies substantially ineffective to influence thereceiver.

From the foregoing explanation, it can be seen that a clear, caution, orstop control or indication may be transmitted at any inductor locationby properly governing the control circuits for the inductor. If it isdesired to provide for all of these controls or indications of clear,caution or stop at the same inductor location, the control circuits areorganized and arranged to be controlled by contacting means, equivalentto the switch 21 as shown in Fig. 1. If this switch 21 is in theposition shown, the coils. on the longitudinal cores TA and TB of theinductor are connected to the coils on the transverse core TC, toprovidefor a clear indication. If the switch 27 is in its intermediateposition, the coils TBI, T32 of the inductor core TB are shor -circuitedby the wires 33, 32, 42, 38 and 35, while the coils TAI and TA2 areclosed through the stop condenser 2|. Thus, the longitudinal core TB ofthe inductor is ren dered ineffective to de-energize'relay RB, while theinductor core TA is effective to de-energize relay RA. This correspondsto caution conditions. If the switch is in the lower open position, thecoils on the longitudinal inductor cores TA and TB are both connected totheir stop condensers 2| and 22; and both relays RA and RB aredeenergized, corresponding to a stop control.

It should be noted that the desired caution control, obtained byde-energization of one of the relays RA or RB, and the stop control,obtained by the simultaneous deenergization of both of these relays RAand RB, will be obtained when the locomotive or car is travelling ineither direction over the track inductor, with either end leading,without any change in the circuit connections either on the car or onthe track. In other words, the receiver and inductor are symmetrical;and no change or adjustment has to be made to provide for operation ofthe locomotive or motor car with either end leading, or for trainmovements in either direction.

Where it is desired to have a caution or a clear indication only at oneinductor location, and a stop control or clear indication at anotherinductor location, such as for a typical home and distance arrangementof signals, the inductor control circuits are arranged as shown in Fig.4. At the distant signal D, a circuit controller 45 operated directly bythe signal, or an equivalent contact of a distant relay, acts underclear conditions to provide a circuit to connect the coils on thelongitudinal inductor cores TA and TB with the coils on the transverseinductor core C; and if the distant signal indicates caution, thiscircuit controller establishes a short circuit for the pair of coils onone of the longitudinal cores, such as the coils 'IAi, TA2, while thecoils on the other longitudinal coil are connected to the stopcondenser, in a manner which will be apparent from the drawings. At thehome signal location, a circuit controller 46 operated by the homesignal, or by home relay, acts to connect the coils on both of thelongitudinal inductor cores to the coils of the transverse core, whenthe home signal is clear, and to connect the coils on both of thesecores to their stopping condensers when the home signal indicates stop.

It will be apparent that other arrangements of control circuits maybeprovided for governing the controlling condition of the track inductorfor the same or different locations, and still carry out the principles.and mode of operation of the invention.

Fig. 5 illustrates a variation or modification of the invention in whichthe receiver has only one longitudinal core A, and the track inductor acorresponding core TA, so that only one restrictive indicationv orcontrol of either stop or caution, as desired, is obtained at aninductor location, in conjunction with a clear indication transmitted byreflecting energy from the receiver to the track inductor and back tothe receiver through the medium of the transverse cores C and TC andtheir coils, in the manner explained.

Other modifications and'variations in the arrangement and positioning ofthe receiver cores on the vehicle may be employed. For example, in

the organization illustrated, the transverse core C is disposed near themiddle of the longitudinal cores A and B; but this transverse core maybe carried at a suitable distance, either ahead or behind thelongitudinal cores, and the inductor cores may be disposed in acorresponding relationship. Such an arrangement more distinctlysegregates the transverse core C magnetically from the longitudinalcores A and B, and assures that any energization of the transverse coremust come from the track. If desired, two such transverse cores may beprovided to co-operate with an inductor for movement of the vehicle ineither direction, or with either end leading.-

Also, it should be understood that the relative spacing, shape, andproportions of the receiver and inductor cores shown is merelyillustrative, and that various other structural organizations may beemployed without departing from the invention. For example, thelongitudinal cores may be spaced farther apart than shown, and thetransverse core C located at a higher plane, if it is desired to provideclearance over water pans or similar objects in the middle of the track.

Having explained how the system of this invention acts to transmitcaution, or stop controls:

or indications from the trackway to a moving vehicle, consideration maynow be given to the manner in which these controls may be utilized toprovide for the desired safety of train operation. One arrangement ofthe car apparatus and circuits for this purpose is illustrated in Fig.6.

Referring to Fig. 6, it is contemplated that the caution control willcause a partial application of the brakes, accompanied by an audiblewarning signal which continues until acknowledged by the engineman ormanual operation of a restoring switch or button; and that the stopcontrol will result in a full or emergency application of the brakes,continued until the train is stopped, and the apparatus restored by areset device, preferably accessible only from the ground.

This scheme of partial or full automatic brake control, while applicableto various types of air brake equipment, is illustrated as applied to asystem of the so-called vacuum type, in which the brakes are applied byadmitting atmospheric air into a brake pipe or its connection. In thisform shown, a caution electro-pneumatic valve CV of suitableconstruction, acts when de-energized to open a valve 50 to allowatmospheric air to pass through a suitable air whistle 5| or equivalentaudible signalling device, into the brake pipe or a connection 52 atsuch a restricted rate as to cause the desired partial application ofthe brakes. The valve is biased to open by a suitable spring 53, whenthe winding of the electropneumatic valve CV is de-energized, aided bythe atmospheric pressure on said valve 50. Another valve 54, closed whenvalve 50 opens, is preferably provided to avoid leakage around the stemof valve 50 and assure passage of air through the whistle 5i. Anothersimilar electro-pneumatic valve SV when de-energized, opens a valve 55,biased by a spring 56, to establish an opening into a similar connection52a to the brake pipe to cause a quick or emergency application of thebrakes.

In addition to these electro-pneumatic valves CV, SV and the relays RAand RB, directly responsive to the caution and stop indication, repeaterrelay RAP and REP, a stop stick relay SR, an acknowledging device AS,and reset switch RS are employed, with contacts and circuit connectionsso organized as to obtain the desired operation. These contacts andcircuit connections are more conveniently considered in describing theoperation. The circuits are illustrated in a simplified and diagrammaticform, with the connections to terminals of a suitable supply of current,preferably direct current, indicated by the symbols and Under normalconditions, while the vehicle is travelling between inductor locationsunder clear conditions as shown in Fig. 6, the repeater relay RAP isenergized by a circuit readily traced from front contact 60 of relay RA,wire 6|, relay RAP to The repeater relay RBP is energized by a similarcircuit from through front contact 62 of relay RB, wire 63, relay RBP,to

With the relays RAP and REP thus energized, the cautionelectro-pneumatic valve CV is maintained energized by a circuit fromfront contact 64 of RAP, wire 65, normally closed contact 66 of theacknowledging switch AS, wire 61, front contact 68 of RBP, wires 69 and10, winding of valve CV, to

The stop stick relay SR is energized by a stick circuit from through afront contact H of the relay RAP, in multiple with a front contact 12 ofthe relay RBP, wires 13 and 14, relay SR, wires 75 and 16, front contact11 of relay SR to With the relay SR energized and the reset switch RS inits normal position shown, the stop electro-p-neumatic valve SV isenergized by a circuit readily traced from front contact '18 of relaySR, wires 19, magnet winding of valve SV, wire 80, and switch RS in thenormal position to Assume now that the vehicle passes a track inductorin the caution condition, i. e. with one or the other of itslongitudinal cores TA and TB eiiective to cause de-energization of therelay RA or RB. Such de-energization of the relay RA, or the relay RB,de-energizes relay RAP or RBP, as the case may be, and breaks at theirfront contacts 64 or 68 the energizing circuit for the caution valve CV,thereby sounding the whistle 5| and making a partial application of thebrakes. This condition continues until the engineman operates theacknowledging or restoring switch AS located within his convenientreach.

This operation of the acknowledging switch AS closes contacts 80 and BIto establish a shunt circuit around the resistances II and I5 in theenergizing circuits for relays RA and RB, so that whichever relay hasreleased its armature may again attract its armature, due to theincreased current, normal current conditions in the alternating currentcircuit having in the meantime been established by movement of thereceiver beyond the influence of the inductor.

When the acknowledging switch AS is thus manually operated to restorethe relay RA or RB, as the case may be, this switch must be returned tothe normal position to close contact 86, in order to energize thecaution valve CV. Consequently, the switch AS cannot be moved or kept inthe restoring position and prevent operation of the caution valve CV.This acknowledging switch AS may be of any suitable construction and isenclosed in a suitable sealed or locked case, indicated by dash lines,with a suitable knob or operating handle projecting outside of the case.This switch is preferably provided with a spring, not shown, forreturning it to the normal position, although it may be operatedmanually to both positions.

If now the vehicle passes a track inductor in its stop position, i. e.with both the inductor cores TA and TB effective, both relays RA and RBare simultaneously de-energized, and in turn their repeater relays RAPand REP, so that the stick circuit for the stop relay SR is broken bythe concurrent opening of the front contacts H and 12 of the repeaterrelays RAP and REP. The de-energization of the stop relay SR breaks theenergizing circuit for a stop valve SV, which causes a full or emergencyapplication of the brakes.

This simultaneous de-energization of relays RAP and REP opens theenergizing circuit for the caution valve CV; and in order that thisvalve CV may not be operated as well as the stop valve SV, asupplemental circuit to hold up the valve CV is preferably provided, sothat when relay SR drops, it closes an energizing circuit for the valveCV from through back contact 18 of relay SR, wires 83 and 70, Valve CV,to

When a stop control has been thus transmitted, the acknowledging switchAS has to be operated by the engineman to restore the relays RA and RB;but the stick stop relay SR is not energized until the reset switch RSis also operated. This reset switch RS is preferably accessible onlyfrom the ground, or otherwise so constructed that it cannot be operateduntil the train has been brought to a stop, or the stop brakeapplication has been maintained for a suificient time. Operation of thereset switch RS closes a pick-up circuit for the stop relay SR over wire84; and this switch must then be returned to its normal position topermit energization of the stop valve SV.

In the arrangement shown in this Fig. 6, the clear indication istransmitted in the same way already described to render the tube VTconductive to allow current to flow in its plate circuit; but in thisembodiment of the invention, a time element device TE is provided toautomatically open this plate circuit after a time and automaticallyrestore the tube to its normal condition to extinguish the lamp G. Inthe simplified form illustrated, this time element device TE comprises asolenoid winding 85, having a core 36, which drives a contact memberthrough a compressible spring 88. The movement of the contact 81 isretarded by a suitable dash pot 89, so that this contact membermaintains engagement with a stationary contact for the desired timeinterval after energization of the solenoid 85. When the tube VTresponds to the clear indication impulse and current flows in its platecircuit to light the lamp G, the solenoid is energized at the same timeand attracts its core 86, stressing the spring 88, and initiating theretarded upward movement of the contact member 81. After the desiredtime interval for which the device is built or adjusted, the contactmember 81 is raised by the coil 85 under the retarding influence of thedash-pot 8!! far enough to separate from the stationary contact 90,whereupon the plate circuit is broken, the tube VT is restored tonormal, and the solenoid 85 is deenergized to cause the contact member81 to drop to its'lower normal position under its own weight,supplemented. by a spring, if desired, ready for the next operation.

In the arrangement of Fig. 6, the plate circuit of the tube VT alsoincludes, in addition to the lamp G and the contacts of the time elementdevice TE, front contacts SI and 92 of the repeater relays RAP and REP,so that the lamp G is not lighted, or at least is very quicklyextinguished, when either relay RAP or RBP, or both, responds to acaution or stop control. This is a supplemental and optional feature,which is considered desirable to assure that no misleading indication ofclear shall be given under either caution or stop conditions, and eventhough the system is otherwise organized, as already explained, suchthat clear indication is not communicated except under clear conditions.

Another organization of relays and circuits for utilizing the cautionand stop control is illustrated in Fig. '7, which incorporates theadditional feature that the engineman or driver must acknowledge thecaution control by timely operation of the acknowledging switch AS,otherwise the stop valve is operated to bring the train to a stop. Inother words, if the engineman is dead, incapacitated, or inattentive tohis duties, and fails to operate the acknowledging switch AS within alimited time after a caution control is received, and thus fails tomanifest that he is aware of the existence of danger and assumesresponsibility for the safe control of the train, then a full oremergency application of the brakes automatically occurs.

This modification of Fig. 7 adds to the same parts and circuits of Fig.6 a timing device, which is initiated upon de-energization of thecaution valve CV, and opens the stick circuit for the stop relay SRafter a time delay, unless the relays RA and RB are restored, and thecaution valve CV again energized, by timely operation of theacknowledging switch AS. In the simplified arrangement illustrated, thistiming device is shown in the form of a slow-release relay TM, which isenergized by the circuit from through a normally closed contact 94operated by the caution valve CV, wire 95, relay TM to and which isprovided with a dash-pot or other well-known means to delay the openingof its front contact 96 for a desired time interval afterde-energization of its winding. The contact 96 of this timing relay TMis included in the wire 14 of the stick circuit for the stop relay SR.

With the organization as shown in Fig. '7, when a caution control isreceived and the caution valve CV is deenergized, in the manner alreadyexplained, the timing relay TM is also de-energized. If the engineman isalive and alert, and promptly operates manually the acknowledging switchAS over and back to restore the relay RA or RB, as the case-may be, andreenergize the valve CV, the timing relay TM is again energized beforesufficient time, such as 10 seconds, has elapsed for the contact 96 ofthe relay TM to open and break the stick circuit for the stop relay SR.If, however, the relay SR is de-energized, the resultant brakeapplication cannot be released until the reset switch, RS is operated.This brake application is in the nature of a penalty to induce theengineman to be alert; and the manual act of the engineman in operatingthe acknowledging switch AS is a definite acknowledgment or recognitionof the existence of danger conditions and assures that the engineman isin full possession of his faculties and may be relied upon to takecharge of the control of the train.

From the foregoing explanation, in connection with the drawings, it canbe seen that a simple and efficient system of intermittent inductivetrain control may be constructed in accordance with this invention,which satisfies the requirements and conditions for practical operation,and which has the various important features and advantages pointed out.

Having now particularly described and ascertained the nature of myinvention and in what manner the same is to be performed, I declare thatwhat I claim is: v

1. In an intermittent inductive train control system, vehicle equipmentcomprising, a control coil in a normally resonant circuit normally en.-ergized with alternating current, normally energized relay meansresponsive to a decrease in the normal current in said circuit, anormally de-energized clear indication receiving coil having the minimumof magnetic coupling with said coil in said circuit; and trackway meanseffective in one controlling condition to influence said control coil onthe vehicle inductively to cause effective de-energization of said relaymeans, and in another clear controlling condition to receive energyinductively from said resonant circuit and induce a momentary voltagepulse in said clear indication coil and without de-energization of saidrelay means.

2. An intermittent inductive train control system for railroadscomprising, normally energized relay means on a vehicle for arestrictive control, a normally de-energized and inactiveelectroresponsive device on the vehicle for a clear indication, areceiver on the vehicle energized from a source of alternating currenton the vehicle of relatively high frequency, and an inductor onthe'track magnetically coupled with said receiver during movement of thevehicle past the inductor location, said inductor in one stoppingcondition causing de-energization of said relay.

means without affecting said electro-responsive device, and in anotherdistinctive clear condition causing momentary energization of saidelectroresponsive device without de-energization of said relay means byenergy derived wholly from said source on the vehicle.

3, An intermittent inductive train control systern for railroadscomprising, a receiver having separate magnetic cores with coilsthereon, said cores being disposed substantially at right angles to havethe minimum magnetic coupling, the coil on one of said cores beingincluded in a normally resonant circuit energized from a source ofalternating current on the vehicle of a relatively high frequency, relaymeans on the vehicle responsive to a decrease of current in said core ofsaid receiver, and a track inductor havsystem of the characterdescribed, a receiver on a vehicle having a magnetic core with a coilthereon in a normally resonant circuit energized from a source ofalternating current on the velicle, normally energized relay meansresponsive to a reduction in the current in said coil, normallyde-energized clear indication receiving means on the vehicle, a trackinductor core magnetically coupled with the core of the receiver duringmovement of the vehicle bythe inductor location and tending to disturbthe resonance of said circuit to cause effective de-energization of saidrelay means, said inductor core having a coil thereon in which voltageis induced by the magnetization of the receiver core, and meansconnected to said inductor coil only under clear traffic conditions forinductively actuating said clear indication receiving means by energyderived wholly from the source on the vehicle and withoutde-energization of said, relay means.

5. An intermittent inductive train control system for railroadscomprising, a receiver on a vehicle having separate coils with theiraxes. at right angles to have minimum magnetic coupling, a trackinductor having coils corresponding to those of the receiver andmagnetically coupled therewith during movement of the receiver by thetrack inductor, a source of alternating current on the vehicle forenergizing one of the coils of the receiver, and a circuit'closed onlyunder clear traffic conditions for connecting together the coils of theinductor, whereby energy from said source is inductively transmittedfrom the receiver to the inductor and back to the receiver to produce aclear indication.

- 6. Apparatus for inductively transmitting indications from the trackto a moving vehicle comprising, in combination with a normally energizedrestrictive indication device and a normally de-energized clearindication device both on thevehicle, of a receiver on the vehicle andan inductor on the track cooperable inductively to cause eitherde-energization' of said normally energized restrictiveindication deviceor the energization of said normally de-energized clear indicationdevice by energy derivedwholly from a source of alternating current onthe vehicle,

said conductor comprising separate coils with their axes at rightangles, and control means for connecting said coils in series or forconnecting one of said coils to a stop condenser.

7. Apparatus for transmitting distinctive caution or stop controlsinductively from the trackway to a moving vehicle comprising, a receiveron the vehicle having duplicate magnetic cores with coils thereon inseparate normally resonant circuits energized from a source ofalternating current on the vehicle of a relatively high-frequency,relaymeans associated :with each of said circuits and independentlyresponsive to the reduction in the current in its circuit, an inductoron the track having cores and coils corresponding with its said receiverand magnetically coupled therewith during movement of the veefiective intheir influence upon the corresponding receiver core to causede-energization of only one, or both, or neither of said relay means.

v8. An intermittent inductive train control system comprising, incombination with vehicle equipment having a normally resonant circuitenergized from a source of alternating current on the vehicle and anormally de-energized clear indication receiving circuit, of trackwaymeans inductively energized from said resonant circuit and effectiveonly if a clear indication circuit on the trackway is closed formomentarily energizing said clear indication circuit during movement ofthe vehicle by said trackway means without materially disturbing theresonance of said circuit.-

9. An intermittent inductive train control sys tem comprising, apparatuson a vehicle including spaced parallel magnetic cores disposed1ongitudinally of the vehicle symmetrically on opposite sides of itscenter line, a transverse magnetic core disposed substantially at rightangles .to said longitudinal cores, coils on said longimeansco-operating inductively with said cores on the vehicle and eifectivedependent upon its controlling condition to cause de-energization of oneor the other or both of saidrelay means or magnetization of saidtransverse core by energy derived wholly from said source on the vehiclewithout de-energization of either of said relay means;

10. Apparatus for inductively transmitting a clear indication from thetrackway to a moving vehicle comprising, in combination with a source ofalternating current on a vehicle, of clear indication receiving meansincluding a magnetic core having spaced normally de-energized coilthereon wound and connected in series such that cumulative voltages areinduced therein only by magnetic flux through said coils in oppositedirections at the same instant, and trackway means effective only when aclear circuit is closed and deriving its energy inductively from saidsource on the vehicle alonefor creating flux fields to induce cumulativevoltages in said coils.

11. A system of intermittent inductive train control comprising, areceiver on a vehicle and an inductor on the track; having counterpart'cores and coils of the same relative dimensions and disposition, saidreceiver and inductor each including a core extending longitudinally ofthe track and symmetrically with respect to the center line of thetrack, and a transverse core disposed at right angles with respect tothe longitudinal core, whereby the inductive co-operation" between saidreceiver and track inductor is the same for either direction of movementof the vehicle with either end leading.

12. A receiver for intermittent inductive train control systems adaptedto be carried on avehicle and comprising, two spaced parallellamidication coil,

nated cores extending longitudinally of the vehicle and symmetrical withrespect to its center line, a transverse core disposed at right anglesto said longitudinal cores near their middle, coils on said longitudinalcores included in separate normal resonant circuits energized from asource of alternating current on the vehicle of a relatively highfrequency, and spaced coils on said transverse core wound and connectedinseries so that cumulative voltages are induced therein only bymagnetic flux through said coils in opposite directions at the sameinstant.

13. A receiver for intermittent inductive train control systemscomprising, a laminated magnetic core, two spaced clear indicationreceiving coils on said core, which are so wound and connected as toproduce cumulative voltages in response only to magnetic flux throughsaid coils in opposite directions at the same instant.

14. Vehicle equipment for intermittent inductive train control systemscomprising, two spaced parallel laminated magnetic cores disposedlongitudinally of the vehicle and symmetrically with respect to itscenter line, a transverse laminated magnetic core disposed at rightangles to said longitudinal cores near the middle, two coils on each ofsaid cores, 2. source of alternating current on the vehicle of arelatively high frequency, the coils on the longitudinal cores beingincluded in separate normally resonant circuits energized from saidsource, relay means associated with each of said circuits andindependently responsive to a decrease in normal current in its owncircuit, normally de-energized and inactive clear indication receivingmeans responsive to a momentary voltage pulse in the coils of thetransverse core, said coils on the transverse core being wound andconnected so that cumulative Voltages are induced therein only bymagnetic flux through said coils in opposite directions at the sameinstant.

15. A track inductor for intermittent inductive train control systemscomprising, two cores positioned to have a minimum of magnetic coupling,coils on said cores, and control means operable to at times connect allof said coils in series with each other and with a clear condenser, andat other times to connect in series the coils on one of said coresalonewhile open circuiting the coils on the other core, and a stop condenserconnected across the last said coils.

16. A track inductor for intermittent inductive train control systemscomprising, two spaced laminated magnetic coils disposed longitudinallyof the track and symmetrically on opposite sides of the center line ofthe track, a transverse core disposed at right angles to itslongitudinal cores, coils on said cores, the coils on the transversecore being spaced and wound and connected in series to create fluxes inopposite directions at the same instant, and controllable means for attimes connecting all of said coils in series with each other and a clearcondenser.

17. A train control system comprising, in combination with a source ofalternating current on a vehicle of a relatively high frequency, areceiver having a normally de-energized clear inquick-actingelectro-responsive means connected to said coil and responsive only to afrequency double the frequency of said source, and means partly on thevehicle and partly on the track and effective only when a clear circuiton the track is closed for producing in said coil a voltage pulse ofdouble frequency derived wholly from said source on the vehicle.

18. An intermittent inductive train control system comprising, a sourceof alternating current on a vehicle, coils on the vehicle energized fromsaid source, a normally de-energized clear indication receiving circuiton the vehicle requiring energization to indicate clear, and trackwayinductor means positioned for receiving energy from said energized coilson the vehicle for inducing a voltage pulse in said clear indicationreceiving circuit of a frequency different from that of said source, andonly if a clear circuit on the track is closed.

' 19. An intermittent inductive system of the character described, asource of alternating current on a vehicle of relatively high frequency,a receiver on the vehicle having coils in a normally resonant circuitenergized from said source, said receiver including a normallydeenergized clear indication receiving means responsive only to afrequency double that of said source, and trackway means inductivelyenergized by said coil in said resonant circuit and effective only if aclear circuit is closed to induce a voltage of double frequency in saidclear indication receiving means during movement of the receiver by saidtrackway means and without materially disturbing the resonance of saidcircuit.

20. An. inductor for intermittent train control systems comprising twomagnetic cores disposed to have a minimum of magnetic coupling with eachother, coils on said cores, a clear indication circuit connecting thecoils on one core in series through a double Wave rectifier, and meansconnecting the output side of the rectifier in series with the coils onthe other core whereby alternating current of a given frequency inducedin the coils of said one core will produce current of double frequencyin the coils of the other core.

21. An intermittent inductive train control system for railroadscomprising, in combination with a source of alternating current on avehicle of a relatively high frequency, a normally deenergized clearingindication receiving circuit, an electronic tube connected to saidreceiving circuit and rendered conductive by a momentary voltage pulse,said tube once rendered conduc- I tive remaining in that state aftercessation of the voltage pulse until restored to normal, and trackwaymeans from said source on the vehicle for inducing a voltage pulse insaid clear indi-, cation receiving circuit only if a clear circuit onthe track is closed.

22. In a system of intermittent inductive train control, apparatus fortransmitting clear indication from the track to the moving vehiclecomprising, in combination with a source of alternating current. on thevehicle, clear indication receiving circuit on the vehicle, a receiveron the vehicle and the inductor on the track co-operable only if a clearcircuit on the track is closed to induce a momentary voltage pulse insaid from the trackway, an electronic tube coupled with said circuitrendered conductive only if its grid. voltage is increased above acritical value, said tube when once rendered conductive remaining inthat state after the voltage pulse has ceased until restored, indicationmeans governed by said tube, and means for automatically restoring saidtube to its normal condition after a predetermined time following eachoperation.

24. Apparatus for inductively transmitting a clear indication from atrackway to a moving vehicle comprising, in combination with a source ofalternating current on the vehicle, a normally de-energized clearindication receiving coil on the vehicle, means including an electronictube responsive to a voltage pulse in said coil only if of a frequencydouble the frequency of said source, and trackway means effective onlyif a clear circuit is closed for inducing a voltage pulse in said coilof said double frequency by energy derived wholly from the source on thevehicle.

25. A system of automatic train control com,- prising, separate relaymeans on the vehicle, a receiver on the vehicle and a track inductorcooperable to inductively cause de-energization of one or both of saidrelay means dependent upon the controlling condition of said trackinductor, a caution control device on the vehicle actuated uponde-energization of either one of said relay means, and a stop controldevice actuated only upon simultaneous de-energization of both saidrelay means.

26. A system of automatic train control comprising, separate relay meanson a vehicle, a receiver on a vehicle and a track inductor includingduplicate magnetic cores and coils co-operable to cause de-energizationof one or both of said relay means dependent upon the condition of thetrack inductor, a caution control device on the device actuated uponde-energization of either one of said relay means, a stop control deviceactuated only upon simultaneous de-energization of both of said relaymeans, said relay means when once operated remaining in that state untilrestored, a manually operable switch for restoring said relay means, anda separate manually reset switch for restoring said stop control device.

2'7. A system of automatic train control comprising, separate relaymeans on the vehicle, a receiver on the vehicle and a track inductorcooperable to inductively cause deenergization of one or both of saidrelay means dependent upon the controlling condition of said trackinductor, a caution control device on the vehicle actuated upondeenergization of either one of said relay means, a stop control deviceactuated only upon simultaneous deenergization of both said relay means,and means for automatically applying the brakes to one extent uponactuation of the caution device, and to a different extent upon theactuation of the stop device.

28. An intermittent inductive train control system comprising a sourceof alternating current on a vehicle, coils on the vehicle energized fromsaid source, a normally deenergized clear indication receiving circuiton the vehicle requiring energization to indicate clear, and trackwayinductor means positioned for receiving energy from said energized coilson the vehicle for inducing voltage in said clear indication receivingcircuit of a frequency difierent from that of said source, and only if aclear circuit on the track is closed.

R IGH RD-

